Mould for continuous casting of metal strips

ABSTRACT

A mould for continuously casting metal strips comprises a pair of side walls ( 11 ) on opposite sides of an open-ended mould cavity (C) having an entrance end (E) for continuously receiving molten metal and an exit end (D) for continuously discharging a moving solidified strip (D) formed from the molten metal. Each mould side wall ( 11 ) includes a graphite block ( 13 ) formed of a stack of a multiplicity of elongate graphite laminae ( 16 ) having opposite faces ( 16 A) and inner edges ( 16 B), said inner edges ( 16 B) jointly forming a surface ( 16 A) directed toward the mould cavity (C). The mould further comprises a cooling system associated with each graphite block ( 13 ) and including coolant tubes ( 15 ) extending through the stack transversely to said opposite faces ( 16 A) of the graphite laminae ( 16 ) forming the stack.

BACKGROUND OF THE INVENTION

This invention relates to a mould for continuous casting of metal stripsand more particularly to a continuous-casting mould of the kindcomprising a pair of mould side walls on opposite sides of an open-endedmould cavity having an entrance end for continuously receiving moltenmetal and an exit end for continuously discharging a moving solidifiedstrip formed from the molten metal, each said mould side wall includinga graphite block, and further comprising a cooling system associatedwith each graphite block and including coolant tubes contacting thegraphite block.

In the art of continuous casting of metals, especially in the continuouscasting of non-ferrous metals or alloys, such as copper or copper basealloys, it is common practice to use a casting mould in which the wallsof the open-ended mould cavity are formed by graphite lining plates,because graphite has advantageous lubricating properties and a fairlyhigh thermal conductivity. These properties are highly desirable,firstly because low friction between the mould cavity walls and themoving solidified strip is essential and secondly because high thermalconductivity is required to permit efficient cooling of the mould andthus rapid solidification of the molten metal continuously fed into themould cavity.

U.S. Pat. No. 3,519,062 and U.S. Pat. No. 3,809,148 A show examples ofmoulds for continuous casting of metal strips in which the inner facesof the side walls of the mould cavity are covered by thin lining platesof graphite. On the side directed away from the mould cavity, thegraphite lining plates engage and are supported by backing and coolingmembers of metal. These backing and cooling members not only support andprotect the graphite lining plate but also serve as cooling jacketsthrough which a liquid coolant is passed to carry away heat from themould cavity via the graphite lining plates.

It is also known, although not common practice, to form the inner facesof the mould side walls from thick graphite blocks or slabs andessentially dispensing with the conventional backing and coolingmembers. Thus, GB 2 034 218 A discloses a continuous-casting mould ofthe kind initially indicated, in which the horizontal mould cavity isdefined by a pair of heavy solid graphite blocks which are placed one ontop of the other and provided with mould cavity defining recesses intheir confronting inner faces. An array of flattened coolant tubes ofmetal are urged against the outer faces of the blocks to be held inclose contact with the blocks to carry off heat transmitted from themould cavity across the thickness of the graphite blocks.

BRIEF SUMMARY OF THE INVENTIONS

An object of the invention is to provide an improved continuous-castingmould of the kind indicated initially which can be produced economicallyand is capable of efficiently cooling the molten metal in the mouldcavity.

In accordance with the invention there is provided a mould forcontinuously casting metal strips, comprising a pair of mould side wallson opposite sides of an open-ended mould cavity having an entrance endfor continuously receiving molten metal and an exit end for continuouslydischarging a moving solidified strip formed from the molten metal, eachsaid mould side wall including a graphite block, and further comprisinga cooling system associated with each graphite block and includingcoolant tubes contacting the graphite block, characterised in that thegraphite block of each of said mould side walls is formed of a stack ofa multiplicity of elongate graphite laminae having opposite faces andinner edges, said inner edges jointly forming a surface directed towardthe mould cavity, and in that the coolant tubes extend through the stacktransversely to said opposite faces of the graphite laminae forming thestack.

The laminated construction of the graphite block lends itself to asimple and economical production. Before the graphite laminae arestacked they are formed with apertures for receiving the coolant tubes,e.g. by punching. Then they are stacked by sliding them over the tubes.When the stacking is completed, the stack, which thus encloses thetubes, is compacted by the application of opposing forces to the ends ofthe stack to force the laminae into close face-to-face contact with oneanother and at the same time bring about a close contact between thelaminae and the coolant tubes.

Preferably, a pair of metal end members are applied to the ends of thestack in face-to-face engagement with the outer face of respective onesof the outermost graphite laminae of the stack. The coolant tubes arepreferably received on the end members. In this manner, the laminaeforming the stack are securely held together by the tubes and the endmembers so that the assembly formed by the stack, the coolant tubes andthe end members can be easily handled as a unit and the faces of thestack can be machined to become smooth.

A particularly efficient heat transfer from the mould cavity to thecoolant passing through the coolant tubes is obtained by forming thestack from laminae made from compacted graphite flakes oriented so as tobe generally parallel to the opposite faces of the graphite laminae.With graphite laminae so made, the heat conductivity in planes parallelto the faces of the laminae is considerably higher than the heatconductivity in the direction perpendicular thereto.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be described in greater detail below with referenceto the accompanying drawings in which an embodiment of thecontinuous-casting mould according to the invention is diagrammaticallyillustrated.

FIG. 1 is a view in vertical section along line I—I of FIG. 1illustrating an example of a continuous-casting mould embodying theinvention, the mould being shown with a tundish and strip that is beingcast;

FIG. 2 is a plan view of the mould shown in FIG. 1, the tundish shown inFIG. 1 being omitted; and

FIG. 3 is a fractional elevational view of one of the two graphiteblocks which form essential parts of the mould shown in FIG. 1.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

In the embodiment of the invention shown by way of example in thedrawings, the continuous-casting mould 10 according to the invention isused for continuous vertical casting of metal strips. As will beappreciated, however, the invention is not limited to vertical casting;the inventive concept is equally well applicable to horizontal casting.

As best shown in FIG. 1, and as is well known in the art, molten metalis continuously poured from a tundish T into a generallyparallelepipedal mould cavity C which extends vertically through themould 10 and is open at the top and at the bottom of the mould. Themolten metal in the tundish T is poured through a nozzle N into theupper or entrance end E of the mould cavity C where it forms arelatively stationary meniscus covered by a liquid flux. During itspassage from the entrance end E to the lower or exit end D of the mouldcavity C the molten metal is cooled by the mould to form a solidifiedstrand S, which is in this case a strip and thus of a width that is alarge multiple of the thickness.

In operation, the mould 10 is mounted between a pair of mounting blocksM of a casting machine, which may be of conventional design. The mouldproper comprises a pair of spaced-apart side walls, generally designatedby 11, and a pair of end walls 12 formed of a pair of graphite bars andbridging the gap between the confronting inner sides of the side walls11 so that the side and end walls 11, 12 jointly define the mould cavityC. FIG. 2 clearly shows the rectangular shape of the mould cavity C asviewed in the direction the cast metal moves through the passage formedby the mould cavity.

The side walls 11 are substantially identical in design. Each side wallcomprises two main parts, namely a graphite slab or block 13 one face ofwhich, the inner face 13A, is directed toward the mould cavity C and theopposite or outer face is directed away from the mould cavity, and abacking plate 14 which is secured to the mounting blocks M and supportsand protects the graphite block 13. The backing plate 14 covers theentire outer face of the graphite block 13 and also engages the endsthereof. The graphite block 13 and its construction is unique and willbe described in detail below, whereas the backing plate 14 may be of asubstantially conventional design and need not be further described.

Associated with each side wall 11 is a cooling system which is largelyconventional except for a part thereof. That part is included in thegraphite block 13 and comprises an array of parallel, coolant tubes 15of metal, such as copper. Other parts (not shown) of the system includemeans incorporated in the backing plates 14 for passing a liquid coolantthrough the graphite block 13. As shown in the drawings, the tubesextend horizontally—that is, transversely to the direction in which thecast metal moves through the mould cavity C—between opposite ends of thegraphite block 15 along a vertical plane approximately centrally betweenthe vertical large faces 13A, 13B of the graphite block 13.

The graphite block 13 of each side wall 11 is formed of a large numberof thin strip-like rectangular elongate thin (thickness e.g. about 1 mm)graphite sheets or laminae 16 which are stacked with their broadsurfaces or faces 16A in engagement with one another and their narrowlongitudinal surfaces or edges 16B jointly forming the broad sides orfaces 13A, 13B of the parallelepipedal slab-like straight stack orgraphite block 13 so formed. The inner face 13A of the graphite block 13mounted in the mould 10 forms one of the sides of the mould cavity C.

Preferably, the laminae 16 are made from flaky graphite, that is,graphite made up essentially of compacted flakes which are oriented suchthat they extend in planes substantially parallel to the faces of thegraphite sheets from which the laminae are cut. Graphite sheets (foilsand plates) that kind are readily available as commercial products. Aparticular attraction of such graphite sheets in the context of thepresent invention is that their thermal conductivity in directionsparallel to the faces is considerably better than their thermalconductivity perpendicular to the faces. Examples of commerciallyavailable graphite sheet products that are suitable for the graphiteblock according to the invention are marketed by Sigri ElektrografitGmbH, Meitingen bei Augsburg, Germany, under the designationsSIGRAFLEX-F (foils) and SIGRAFLEX-L (plates).

For the purpose of the present invention, namely to achieve asfavourable heat conducting properties as possible, it is desirable thatthe density of the graphite making up the laminae be as high aspossible. It may be advantageous, therefore, to increase the density ofthe commercially available sheets of flaky graphite by subjecting thesheets, or the laminae cut from them, to a densifying treatment, such asby rolling, before the stacks are formed.

Before the graphite block 13 is formed by stacking the laminae 16,apertures are formed, e.g. punched in the laminae to allow for receptionof the coolant tubes 15. The size of the apertures should be accuratelymatched with the size of the coolant tubes 15 so that a snug fit of thetubes in the apertures is achieved. Such a fit is essential to obtain anefficient heat transfer from the graphite to the liquid coolant flowingin the coolant tubes.

A convenient procedure for forming the stack from the apertured laminae16 is to secure one end of the coolant tubes 15 to an end member 17,preferably a rectangular plate of approximately the length and width ofthe laminae 16 (see FIG. 3 where the thickness of the lamina isexaggerated in the interest of clarity), such that the tubes extend inaccurately parallel relation, and then sliding the laminae 16 over theopposite ends of the tubes and pushing them along the tubes until theyare in face-to face engagement with one another. When all laminae 16required to form the stack have been added, a similar end member 17 isapplied to the stack and pressure is applied in opposite directionsthrough the end members to compact the stack and the laminae 16 formingthe stack.

Such compaction enhances the contact of the lamina with the coolanttubes 15 and thereby promotes the heat transfer from the lamina 16 tothe coolant flowing in the tubes.

Following the above-described assembly of the graphite block 13 with thecoolant tubes 15 accommodated in it, the large faces 13A, 13B of thegraphite block are machined, such as by milling, so that the graphiteblock is reduced to the proper accurate dimensions and will have smoothsurfaces. The so finished block is then mounted to its backing plate andinstalled in the casting machine. The plate-like end members 17 shown inthe drawings, which engage the outer faces of the end or outermostlaminae 16C (FIG. 3) of the stack, may form parts of or be joined withhousings (not shown) in which the ends of the coolant tubes 15 receivedin the end members are connected to suitable means for passing thecoolant through the coolant tubes.

As described above, the confronting faces 13A of the graphite blocks 13form parts of the walls of the mould cavity C. It is within the scope ofthe invention, although not preferred, to line the graphite blocks 13with thin, e.g. 3 mm thick lining plates of graphite.

Although the graphite block 13 is illustrated and described as acomponent of a continuous-casting mould, its applicability as a coolingdevice extends to other applications. Accordingly, the cooling deviceformed by the graphite block 13 is within the scope of the invention asclaimed independently of its use in a particular application, whether inthe metal-processing field or otherwise.

1. A mould for continuously casting metal strips, comprising a pair ofmould side walls on opposite sides of an open-ended mould cavity havingan entrance end for continuously receiving molten metal and an exit endfor continuously discharging a moving solidified strip formed from themolten metal, each said mould side wall including a graphite block and acooling system including coolant tubes, wherein the graphite block ofeach of said mould side walls is formed of a stack of a multiplicity ofelongate graphite laminae having opposite faces and inner edges, saidinner edges jointly forming a graphite surface directed toward the mouldcavity, and wherein each elongate graphite laminae has one or moreapertures through which said coolant tubes are received such that thecoolant tubes extend through the stack transversely to said oppositefaces of the graphite laminae forming the stack.
 2. A continuous-castingmould as claimed in claim 1, including a pair of metal end members inface-to-face engagement with the outer face of respective ones of thetwo outermost graphite laminae of the stack, the coolant tubes beingreceived in said end members.
 3. A continuous-casting mould as claimedin claim 1, wherein the graphite laminae of each stack are oriented suchthat their inner edges extend between the entrance and exit ends of themould cavity, the coolant tubes extending transversely of the directionof movement of the strip discharging through the exit end of the mouldcavity during operation of the mould.
 4. A continuous-casting mould asclaimed in claim 1 wherein a pair of opposed end walls of the mouldcavity are formed by a pair of graphite bars bridging the gap betweensaid side walls along the ends of the stacks of graphite laminae.
 5. Acontinuous-casting mould as claimed in claim 1 including for each ofsaid mould side walls a mould cavity lining member formed of a thingraphite plate supported by said stack of laminae.
 6. Acontinuous-casting mould as claimed in claim 1 including for each stackof graphite laminae a stack-supporting plate substantially coextensivewith the stack.
 7. A continuous-casting mould as claimed in claim 1wherein said graphite laminae are made of compacted graphite flakesoriented so as to be generally parallel to said opposite faces of thegraphite laminae.